This custom cable modem my ISP gave to me does not support forwarding an external port to a different internal port. (For example, I can't forward an incoming connection on port 80 to port 3389 on my main box and and an incoming connection on port 21 to port 3389 on my old box. I need to do this to avoid port blocking.)

I know I could go around this by changing the port of RDP on my machines but I can't because I already have an HTTP server which must run on 80 for internal testing purposes.

I could not find any software updates, I could not get any support from my ISP and I could not find any better cable modems. (Cable modems are very uncommmon compared to ADSL modems.)

Can you put your own router and switch in between your computers and the modem?
–
Shane WealtiFeb 2 '12 at 22:43

How will that work? I don't know how to setup such a network. I have a Linksys WAG160N which was my old ADSL modem. Could that work?
–
AlicanCFeb 2 '12 at 23:04

1

shane is kind of right.. If you put something in the middle, the thing should be a Plain Router, not a Modem/Router device(i.e. not a router with modem built in). A plain Router instead of an adsl modem built in, has an ethernet socket labelled WAN, and that's where you use a cat5 cable to connect your modem to it.
–
barlopFeb 2 '12 at 23:23

Actually you can possibly use an adsl router for that. You use a cat5 cable to connect the modem to a regular port on your modem/router.
–
barlopFeb 2 '12 at 23:25

My old ADSL modem doesn't have it. (Because why would I connect another modem to it right? :P) So should I get something like Linksys E1200?
–
AlicanCFeb 2 '12 at 23:29